class Solution {
public:
    int bfs(vector<vector<int>>& grid)
    {
        queue<pair<int,int>> q;
        int step=1;
        if(grid.size()==1)  return 1;
        q.push(make_pair(0,0));
        int dx[]={0,0,1,1,-1,-1,1,-1};
        int dy[]={1,-1,1,-1,-1,1,0,0};
        while(!q.empty())
        {
            int n=q.size();
            step++;
            for(int j=0;j<n;j++)
            {
                int x=q.front().first;
                int y=q.front().second;
                q.pop();
                // cout<<x<<' '<<y;
                for(int i=0;i<8;i++)
                {
                    int nx=x+dx[i];
                    int ny=y+dy[i];
                    if(nx<0||ny<0||nx>=grid.size()||ny>=grid.size())
                        continue;
                    if(nx==grid.size()-1&&ny==grid.size()-1&&grid[nx][ny]==0)
                    {
                        return step;
                        break;
                    }
                    else if(grid[nx][ny]==0)
                    {
                        grid[nx][ny]=1;
                        q.push(make_pair(nx,ny));
                    }
                }
            }
        }
        return -1;
    }
    int shortestPathBinaryMatrix(vector<vector<int>>& grid) {
        if(grid.empty()) return -1;
        if(grid[0][0] == 1 || grid[grid.size()-1][grid.size()-1] == 1)  return -1;
        return bfs(grid);
    }
};
